Day 2: The Air we Breath

Key Concepts

Question of the Day

What will become of human beings if the phytoplankton and rainforests continue to diminish at current rates?

Lesson of the Day

Running a marathon a day for a week is a challenge, even at sea level. Running at 12,000 feet in the Peruvian Andes, where there is 35% less oxygen in every breath, the challenge becomes even greater. Human cells ‘burn’ oxygen to generate energy, creating an oxygen deficit in cells. The low oxygen content of cells draws a steady flow of oxygen from the blood stream. The blood stream in turn is always being depleted of oxygen by hungry cells, so a steady flow of oxygen from the oxygen-rich air inhaled into the lungs is drawn to the depleted blood stream. The movement of oxygen is like a river that flows continuously downstream, from the air, to the lungs, to the bloodstream, to the cells, where the oxygen is consumed. Without this cascade of oxygen into our cells human beings would not survive, meaning that the production of oxygen is one of the most valuable ecosystem services nature provides.

How Does Nature Create Oxygen?

The oxygen that we breath to power our cellular function is molecular oxygen which is composed of two oxygen atoms bound together (O2).  Molecular oxygen is a waste product of photosynthesis, the process used by plants, algae and some types of bacteria  to take light energy and convert it into chemical energy. A simplified equation for photosynthesis is:

CO2 + H2O + light → Carbohydrates + O2

Roughly half the worlds O2 is produced by photosynthesis on land by trees, shrubs, grasses and other plants. Because of the high density of plant growth, a significant proportion of the terrestrial oxygen produced on the planet comes from the world’s rain forests. The other half is produced by phytoplankton in the world’s oceans.  Phytoplankton and terrestrial green plants maintain a steady balance in the amount of the Earth's atmospheric oxygen, which comprises about 20 percent of the mix of gasses in the atmosphere.   

Before photosynthesis evolved there was no molecular oxygen on the planet Earth. Early life forms on the planet were not reliant on oxygen for survival (anaerobes).  Oxygen began accumulating in the atmosphere with the development and success of photosynthetic organisms about 250 billion years ago, and has fluctuated in atmospheric concentration ever since.

Today human activity is threatening the two main producers of oxygen, rainforests and phytoplankton.  Over 50% of the world’s rainforests have been destroyed in modern times. Even more alarming, a recent study published in the journal Nature reveals that world phytoplankton concentrations have declined by as much as 40% in the past sixty years (see: phytoplankton). This is a concern because phytoplankton, which capture the sun’s energy through photosynthesis, form the basis of the marine ecosystem.  A decline of phytoplankton affects everything up the food chain, including humans. The loss of phytoplankton would have grave consequences for marine life forms, as well as terrestrial life that rely upon marine plants and animals as a food source. The loss of phytoplankton is thought to be a function of the acidification of the oceans which is a byproduct of the release of more CO2 through the burning of fossil fuels.


There have been slight observed decreases in atmospheric oxygen in the past twenty years, although the absolute amount is minimal. Despite the changes seen in rainforest size and phytoplankton concentration predicted fluctuations in O2 levels from ecosystem alterations are not expected to be enough to effect human health.

Although the production of O2 may remain abundant the question remains what is the value of the provisioning of oxygen to human beings?  Currently naturally occurring oxygen is free.  How does this reflect upon mankind’s approach to this essential resource?

Words to Run By

Daily Dispatch

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Video of the Day

Photo of the Day

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Expert Video

School Activities

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Youth Ambassador Activity

Every day of the expedition the Youth Ambassadors will calculate daily the partial pressure of oxygen at their location at the start of the day.  They will compare this to their oxygen saturation and to how they feel running.  They will graph these results.

On day four they will consider where oxygen comes from.  They will consider the following questions: